Thin palladium composite membranes were prepared by modified electroless plating method on α-alumina supports and a dense Pd/α-Al2O3 composite membrane with high hydrogen flux, good selectivity for hydrogen was obtained. It was tested in a single gas permeation system for hydrogen permeance and hydrogen selectivity over nitrogen. The hydrogen permeance of the corresponding membrane was as high as 2.45×10-6 mol·m-2·s-1·Pa-1 and H2/N2 selectivity over 700 at 623K and a pressure difference of 0.1MPa. The main resistance of the composite membrane to H2 permeation lies in the aluminum ceramic support rather than the thin Pd layer.